When fabricating an inorganic material thin film of metal, oxide, nitride or the like, the vacuum deposition method, the sputtering method, the chemical vapor deposition method (CVD method) and the like are primarily used.
With the vacuum deposition method and the sputtering method, a block or a plate of metal or oxide as the raw material for deposition is set in a chamber (vacuum vessel), the inside of the chamber is evacuated, an inert gas such as argon or nitrogen or a reactive gas such as oxygen is supplied to maintain the inside of the chamber at a given pressure value, the raw material solid is gasified through heating or sputtering, and then the resulting material is deposited on a substrate disposed at a prescribed position in the chamber.
Meanwhile, with the CVD method, a raw material gas is introduced in an evacuated chamber, the gas is decomposed by plasma or heat, and then a thin film is deposited on a substrate. With these methods, it is possible to deposit a thin film uniformly across the entire area of a large-area substrate of which one side is several cm to several ten cm, and these are effective methods that are being used industrially.
Nevertheless, now that the needs for a lighter, thinner, shorter and smaller device are high, demands for the development of technology capable of depositing an inorganic thin film having gas sensor capability and conductive property only on a minute area of several hundred micron to several millimeter square are increasing. With these methods based on conventional technology, it is standard to mask the substrate and then perform vapor deposition, sputtering, or CVD. However, these methods are highly inefficient since the raw material consumption in relation to the deposited area is high, and are extremely uneconomical.
In addition, since these methods require a process to be performed in the vacuum device, it is necessary to introduce a substrate in the chamber, evacuate the chamber, perform gas displacement and so on, and these processes require much time.
Meanwhile, with the method employing a plasma having a diameter of several hundred microns to several mm which can be stably generated under atmospheric pressure, it is possible to directly deposit a material only on a minute area of several hundred μm to several mm square on the substrate, and is considered to be an effective technique for dramatically reducing raw material consumption in comparison to conventional methods. In addition, since the plasma can be generated in the atmosphere, the entire process can be completed in a short period of time. In light of these circumstances, thin-film fabrication technology using a plasma jet that is generated inside and ejected from a nozzle having a diameter of several hundred microns to several mm disposed in the atmosphere has been proposed in the past several years.
Non-Patent Document 1, Non-Patent Document 2 and Patent Document 1 disclose a manufacturing apparatus of a carbonaceous thin film based on the CVD method by using a nozzle-type atmospheric-pressure plasma generator and hydrocarbon gas such as methane.
Moreover, Patent Document 2 proposes technology of irradiating the desired position of an amorphous substrate with a plasma jet generated under atmospheric pressure, and melting and recrystallizing the irradiated area. This technology is a thin film process that uses the plasma generated under atmospheric pressure as the heat source.
Although these methods are effective as technology to fabricate thin-film only on a minute area in the atmosphere, they encounter the following technical restrictions. Specifically, with the method described in Patent Document 1, since the raw material to be supplied to the apparatus is a gaseous species, when considering the processes to be performed in the atmosphere, it is not possible to use a gaseous raw material that is harmful to the human body or the environment. With the process for preparing a metallic thin film from a gaseous raw material, since toxic gas such as organometallic gas is used, the types of thin films that can be fabricated by the method described in Patent Document 1 will be limited.
Further, although the method described in Patent Document 2 is a method that utilizes the heat and high activity of plasma in order to improve the film quality in the atmosphere, it does not relate to technology for depositing a heterogeneous material on the substrate.
As a means for overcoming these problems, the present inventors proposed new technology in Non-Patent Document 3 and Patent Document 3. With these technologies, a metal wire as the raw material is preliminarily inserted into a narrow tube for plasma generation, the metal wire is evaporated or melted with the thermal conduction or the like from the generated plasma, the generated gas phase or droplets are condensed or solidified downstream, and deposited on a substrate disposed downstream of the narrow tube outlet.
However, these methods deposit metal or a material having metal as its primary component in a dot shape having a diameter of 1 to 100 μm and a line shape having a width of 5 to 50 μm on a low-melting-point substrate of which the melting point is 500° C. or lower.
In order to prevent damage to the low-melting-point substrate caused by the heat flux from the plasma, the heat capacity is lowered by reducing the diameter of the plasma to be 100 μm or less. With these methods, the particles generated in the narrow tube will be ejected from the narrow tube, and collide with and be deposited on the substrate surface. In other words, the reaction involved with the size, form, composition and the like of the particles is completed within the narrow tube. After the particles are deposited on the substrate, the characteristics of the particles will not change due to the effect of the plasma. Thus, from the objective of preventing damage of the low-melting-point substrate, this technology aims to reduce the influence of the plasma on the substrate, and specializes in depositing a material on an area having a diameter of 100 μm or less.
In the thin-film fabrication process, the adhesiveness between the thin film and the substrate is an important factor. With the dry process in a vacuum as represented by vacuum deposition, sputtering, ion plating and the like, as a method of improving the adhesive strength of the film, means such as heating the substrate using a substrate heating stage or improving the kinetic energy of the deposition material is being used. In addition, with the dry deposition process under atmospheric-pressure, the thermal spraying method of melting and depositing the deposition material is employed.
With the technology described in Patent Document 3, the substrate surface that is slightly melted and roughened by the heat flux from the plasma is contributing to the adhesiveness of the deposition material. However, although this is effective in a substrate having a melting point of 500° C. or less, the same effect cannot be expected in a high-melting-point substrate of silicon, ceramics or the like.    [Non-Patent Document 1] Y. Shimizu et al. J. Phy. D: Appl. Phys., 36, 2940 (2003)    [Non-Patent Document 2] T. Kikuchi et al. J. Phy. D: Appl. Phys., 37, 1537 (2004)    [Non-Patent Document 3] Y. Shimizu et al. Surf. Coat. Technol., 200, 4251 (2006)    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-328138    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2006-060130    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2005-262111